In this context, the company Macromedia has defined a file format known as SWF which describes time animations of multimedia data from vectorial data. An animation contained in an SWF file is generally referred to as “Flash” data.
When a client terminal receives an animation contained in an SWF file, it in fact receives minimal data which makes it possible to reconstruct only part of the images, referred to as key images. The key images are typically the initial image, the final image and intermediate images distributed in the animation.
The client terminal decodes these data and calculates the other images of the animation by interpolation, so as to be able to play the animation at a predefined rate.
However, in order to minimize the size of the SWF file, the latter does not strictly speaking contain the coding data of the key images but only the requests to be sent for downloading the corresponding data.
Under these circumstances, it may happen that the client terminal does not actually receive at an appropriate time all the key images which it needs to reconstruct the animation. The interpolation is then interrupted and the display of the animation freezes.
Furthermore, well-known interpolation techniques would send all requests, thereby wasting some network bandwidth if some key images were received too late to be used for interpolation.